Fiber optic illumination bundles are commonly used to transmit light for illumination into restricted areas. Typical fiber optic illumination bundles are comprised of many hundreds or thousands of individual fiber optics bunched together to form a single light-transmitting bundle. Each fiber of the illumination bundle transmits light individually through the principle of total internal reflection, while the full bundle efficiently transmits large amounts of light from a source to the area to be illuminated. Fiber optic illumination bundles find use in medical devices such as arthroscopic probes and cameras, dental probes and cameras, and inspection probes for mechanical equipment.
Often it is necessary or desirable to have two separate fiber optic illumination bundles used together in close proximity to one another. It is generally advantageous to position such separate illumination bundles in such a manner that they form one cable for ease of use and handling. One common method of accomplishing such cabling is to individually jacket each bundle and twist one about the other, forming a twisted pair of illumination bundles. This method produces a large cable, the diameter being at least equal to the sum of the diameters of the individually jacketed illumination bundles. The large diameter results in a lack of flexibility, excess stress on the outer fiber optic strands, excess losses due to macrobending of the strands, as well as losses due to the extra fiber length required by the helical path of each bundle in the twisted construction. Another method of cabling separate illumination bundles is to jacket them as two pods of a flat cable, the jacket also forming a web between the pods. Again, such an arrangement results in a cable with a maximum cross-sectional dimension equal to at least twice the sum of the diameters of the component illumination bundles. Also, such a cable is not as flexible and usable as a round cable. A third method of grouping two separate illumination bundles into one cable is to simply bunch the two illumination bundles into one large bundle, being careful to keep each component bundle separate at the ends for termination. This method results in a smaller cross-sectional area than the first two methods, but has one major problem. When two illumination bundles are placed in contact with each other, light will be coupled into one bundle from the other where the fiber optics of the respective bundles are in contact with each other down the length of the cable. This coupling is known in the art as cross-talk. For bundles of reasonable size and usable lengths, cross-talk results in appreciable amounts of light leaving one bundle into the other. This loss of light from one bundle, and gain of unwanted light into the other is unacceptable, especially in applications where the fiber optic bundles are used in light sensing measurements.
The cable of the invention provides an improved solution to these problems, by providing a highly flexible cable of low cross-sectional area which does not allow the coupling of light from one illumination bundle to another.